Assessememt of the SPH method: Simulation of simple body shapes impacting on water and a PUMA helicopter ditching

Abstract

The SPH (Smooth Particle Hydrodynamic) method is evaluated through the simulation of water impact tests of rigid cylindrical and triangular bodies performed at Politecnico di Milano [1]. Simulated configurations include 4.4 m/s and 7.7 m/s impact velocities for a wedge and a half-cylinder respectively. The agreement with the test data is very satisfactory, insofar numerical results are proved to be in the order of magnitude of the experimental data. In particular, the simulations are able to predict the acceleration peaks and pulse durations whereas they capture the order of magnitude of the pressures. In parallel to these simulations at the sub-component scale, works also aim at applying the numerical tools to the modelling of a full-scale helicopter ditching, in order to evaluate the codes capacities to handle with industrial problems. The selected application case is the PUMA helicopter, whose FE-model is defined in order to be representative of the real structure in terms of global mass and position of the centre of gravity. The investigated impact configurations include vertical impacts (4 m/s as vertical velocity, 1° as pitch angle) and oblique impacts (4 m/s as vertical velocity, 10 m/s as forward velocity, 5° as pitch angle). As a comparison with the FE tools, simulations are performed by EUROCOPTER with the internal code DITCHER, which is basically used to design floatation devices of helicopters. In this code, calculations are performed on the basis of hydrodynamic equations, validated for FAR impacts by comparison with tests. DITCHER results include positions/velocities/accelerations at the centre of gravity, attitudes/angular velocities/accelerations of the helicopter, and the loads and moments acting on the fuselage. Comparisons with the DITCHER data provide variable agreements depending on the simulated configurations and the compared data.